Discriminating an edge direction at each pixel of an image allows the subsequent image processing steps, for example, denoising, to be simplified while maintaining structural attributes of the image; therefore, Japanese Unexamined Patent Application, Publication No. 2008-293425 (PTL 1) has been proposed as an example of a technique relating to edge-direction discrimination.
Specifically, PTL 1 discloses a denoising device in which an input image signal is subjected to multiresolution conversion to generate a plurality of band image signals that have frequency bands different from each other, and a first image signal that includes information about the frequency bands of the band image signals and frequencies lower than the frequency bands and a second image signal that includes information about frequencies lower than the frequency bands of the band image signals are used to discriminate the directions of edge components in the band image signals and also to denoise the band image signals according to the directions of edge components.